The present invention generally relates to the art of substrate processing and more particularly to a substrate processing method used for forming an insulation film in the fabrication process of a semiconductor device.
With increase of performance in recent semiconductor devices, there arises a situation with such recent high-speed semiconductor devices that use a multilayer interconnection structure in that interconnection patterns in the multilayer interconnection structure are disposed close with each other as a result of device miniaturization. Associated with this, there is caused a problem of wiring delay by the parasitic capacitance formed between these interconnection patterns. Such parasitic capacitance changes in inverse proportion to the distance between the interconnection patterns and is proportional to the specific dielectric constant of the insulation film existing between the interconnection patterns.
Thus, in order to solve the problem of wiring delay in the multilayer interconnection structure and to decrease the parasitic capacitance therein, investigations are being made to use a material of low specific dielectric constant (low-K) in the multilayer interconnection structure for the interlayer insulation film.
The specific dielectric constant of a CVD-SiO2 film that has been used conventionally as an interlayer insulation film is about 3.5-4. Thus, in order to decrease the specific dielectric constant further, it is practiced in the art to add fluorine to the CVD-SiO2 film to form an SiOF film. With this approach, however, it is difficult to attain the specific dielectric constant of lower than the 3.3-3.5, while this degree of decrease of the specific dielectric constant is not sufficient for recent high-density semiconductor integrated circuit devices, and there are cases in which necessary operational speed is not attained.
Thus, there is proposed an insulation film of further lower dielectric constant formed by plasma CVD process with the use of organic silane gas or an insulation film formed by SOD (spin-on-deposition) process, to provide a so called low-K interlayer insulation film. Further, there is proposed a porous film, in which any of these films are made porous. Thus, intensive efforts are being made to develop a low-K interlayer insulation film having a specific dielectric constant of 2.5 or less.
It should be noted that an insulation film formed by a plasma CVD process has a large dielectric constant immediately after the film formation process thereof, and thus, there are cases in which it becomes necessity to reduce the specific dielectric constant by way of predetermined processing such as plasma processing, or the like. Further, such low-K insulation film formed by a plasma CVD process tends to suffer from the problem of poor mechanical strength, and there are cases it is necessary to improve the mechanical strength by way of predetermined processing.